1. Field of the Invention
The present invention relates to an electric power charge and discharge system. In particular, the present invention relates to an electric power charge and discharge system which supplies electric power to a battery noncontactly by receiving a wireless signal.
2. Description of the Related Art
Various electronic devices are coming into wide use, and a wide variety of products are in the marketplace. In particular, in recent years, the spread of portable electronic devices for outdoor use has been remarkable. For example, mobile phones, digital video cameras, and the like have become very convenient because of high-definition display portions, increased durability of batteries, and further reduction in power consumption. A portable electronic device has a structure in which a battery that is a charging means is incorporated. Power source voltage for driving the portable electronic device can be ensured by the battery. As the battery, a secondary battery such as a lithium ion battery has been used, and the battery has been charged directly from an AC adaptor which is plugged into an AC power supply which is wired inside a building or the like (hereinafter referred to as a fixed power supply) (see Patent Document 1: Japanese Published Patent Application No. 2005-150022).
In addition, research on simple charging of a battery with a noncontact means, in which electromagnetic coupling is used with an external electric power supply means has been performed (see Patent Document 2: Japanese Published Patent Application No. 2001-190029).
However, while the frequency in use of electronic devices such as mobile phones, digital video cameras, and the like has been rising and the demand for improvement of hours of use of a battery has been increasing, improvement of charging capability of the battery in accordance with the hours of use of the battery has limitations. Further, the AC adaptor for charging the battery which is a power supply incorporated in such a mobile phone, a digital video camera, or the like is too large to be carried along easily.
Further, noncontact charging utilizing electromagnetic coupling can be performed only in the periphery of a battery charger, and moreover, electric power is needed to be supplied from a fixed power supply. Therefore, it may be necessary to carry the battery charger along, and the burden caused by doing so remains.
In addition, unlike the case where electric power is supplied from a fixed power supply, the electronic devices having the battery continuously consume electric power accumulated in the battery and the hours of use has limitations. Therefore, there is a problem in that improvement of hours of use of the battery largely depends on the improvement of charging capability of the battery and long hours of use of the electronic devices has limitations.